Research On Indoor Visible Light MIMO Communication Technologies

Visible light communication (VLC) technology is a kind of newly developed wireless optical communication technology which receives world-wide attention due to the trend towards green lighting. When multiple LEDs are deployed in indoor environment, there are multiple benefits. It is possible to improve system spectrum efficiency by applying spatial multiplexing or MIMO precoding algorithms. What’s more, the VLC channel will become more robust against interference and blocking. The illumination requirements can be satisfied better as well by properly optimizing the transmit power of LEDs. This thesis focuses on investigating multiple-input multiple-output (MIMO) VLC technologies from four aspects. The visible light communication channel, the optimization of VLC system parameters, VLC MIMO precoding and power allocation algorithms and channel state information estimation are investigated.The analysis of VLC channel is vital for the research of VLC technologies, so the characteristics of indoor VLC channel is analyzed. The channel is modeled and simulated for further studies. Secondly, VLC system parameters such as LED power and half power semi-angle affect the communication performance of VLC systems. The optimization of these parameters is investigated in this part. An LED power optimization algorithm is proposed to improve indoor power and illumination coverage. The influence of different LED half power semi-angle and receiver field of view on VLC systems is also analyzed. Thirdly, since improving communication data rate as well as satisfying indoor illumination requirements are two key problems to be solved for VLC systems. We propose a multi-user precoding and power allocation algorithm for two cases. The first case considers maximum system throughput and illumination optimization. The second case considers maximum fairness and illumination optimization. Lastly, visible light channel state information (CSI) is essential when applying VLC MIMO techniques. When massive LEDs are deployed in indoor environment, a method to estimate visible light CSI is proposed based on indoor positioning which could be a candidate to the estimation of indoor visible light CSI.